State-of-the-art automotive engine control includes on-board diagnosis of various engine components or sensors, particularly when improper operation of such components or sensors can adversely influence various aspects of engine operation and/or emissions. For example, proper operation of an engine cooling system may be ascertained by diagnosis of whether the engine thermostat is operating correctly (e.g., not stuck open or closed), and if the engine coolant temperature sensor is providing accurate readings. In such an example, if a fault is indicated in one or more of the thermostat or engine coolant sensor, a vehicle controller may store the fault information and activate a malfunction indicator light (MIL) alerting the vehicle operator to service the vehicle.
As an example, automotive diagnostic regulations require the engine cooling system to be monitored for achieving a predetermined coolant target temperature during a predetermined engine warm-up interval. In one example, a thermostat may be considered malfunctioning if the coolant temperature does not reach a specified target temperature within a specified time period after the engine is started. In another example, the engine cooling system may be monitored for achieving a stabilized minimum temperature that is needed for the fuel control system to begin stoichiometric closed-loop operation (e.g., closed-loop enable temperature), within a manufacturer approved time interval after starting the engine. If measured engine coolant temperature does not reach the temperature needed for stoichiometric closed-loop operation, wherein stoichiometric closed-loop operation comprises feedback control of an air/fuel mixture combusted in the engine where a 14.7:1 air/fuel ratio is commanded, a fault may similarly be indicated.
Engine coolant temperature monitoring during engine warm-up conditions may in some examples be based on models to infer engine coolant temperature. For example, U.S. Pat. No. 7,921,705 teaches an engine coolant temperature estimation system comprising a coolant temperature estimation module and a coolant monitoring module. The coolant estimation module estimates an engine coolant temperature based on at least mass air flow, vehicle speed, and ambient temperature. The coolant monitoring module selectively operates a vehicle engine based on the estimated engine coolant temperature. Similarly U.S. Pat. No. 6,302,065 B1 teaches estimating engine coolant temperature based on engine thermodynamic properties, such as net engine torque, air-fuel ratio, engine speed, exhaust gas temperature, etc.
However, the inventors herein have recognized potential issues with such methods. For example, the inventors have recognized that under certain ambient temperature conditions, engine coolant temperature inference models may become inaccurate. As such, the use of an engine coolant temperature inference model under certain ambient temperature conditions may potentially result in falsely diagnosing aspects of engine cooling system function. Furthermore, the above-referenced methods do not teach methodology for continuously monitoring aspects of the vehicle engine coolant system during the course of a drive cycle wherein the engine is used to propel the vehicle.
Thus, the inventors have developed systems and methods to at least partially address the above issues. In one example a method is provided, comprising in a first condition, detecting an engine coolant system malfunction based on an engine coolant temperature inference model, and in a second condition, detecting an engine coolant system malfunction based on a time-based monitor.
As one example, the first condition includes an ambient temperature above 20° F., and the second condition includes an ambient temperature below 20° F. In some examples, the second condition includes an engine start event, where activating the time-based monitor is further based on one or more of engine speed and/or engine load above predetermined thresholds, wherein a fault is indicated responsive to an engine coolant temperature below a predetermined threshold when the time-based monitor expires. In this way, correct diagnosis of engine cooling system function may be accomplished, under conditions wherein engine cooling system function may be incorrectly diagnosed if an engine coolant temperature inference model were relied upon.
In another example, a method is provided, comprising during a first mode of operation of an engine, predicting when temperature of a coolant of the engine exceeds a threshold temperature, wherein the predicting is based on an engine coolant temperature inference model; indicating proper operation of a thermostat regulating flow of the coolant in response to an actual coolant temperature exceeding the threshold; and continuing to monitor for the actual coolant temperature exceeding the threshold after the first mode of operation. As one example, the method includes responsive to an indication of the actual coolant temperature dropping below the threshold for a first predetermined time duration (e.g., reset stabilization) after the first mode of operation, initiating a call to reinitiate the first mode of operation to predict when temperature of the coolant exceeds the threshold temperature, indicating proper operation of the thermostat responsive to actual coolant temperature exceeding the threshold temperature, and wherein initiating the call to reinitiate the first mode of operation occurs any number of times actual coolant temperature drops below the threshold for the first predetermined time duration during a drive cycle. In one example, reinitiating the first mode of operation commences subsequent to a second predetermined time duration (e.g., inference stabilization), the second predetermined time duration greater than the first predetermined time duration, and wherein the predicting when temperature of the coolant of the engine exceeds the threshold temperature is suspended during the second predetermined time duration. In this way, by initiating a call to reinitiate the first mode of operation only after the first predetermined time duration (e.g., reset stabilization), false resets to the first mode due to oscillations/fluctuations around the threshold may be prevented. Furthermore, by only reinitiating the first mode of operation subsequent to a second predetermined time duration (e.g., inference stabilization), false fail calls may be prevented, as methods for predicting when temperature of the coolant of the engine exceeds the threshold temperature are very sensitive to any engine speed and/or load changes close to the threshold. Accordingly, continuous monitoring of a vehicle thermostat during the course of a drive cycle may be accomplished, while false resets and fail calls may be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.